The invention relates to a polarizer in particular for the polarization of ultraviolet light with large apertures, with light-permeable, preferably plane-parallel plates which in each case are arranged at an angle to the light incident preferably parallel to the optical axis.
Furthermore the invention relates to a projection apparatus and a device for the photo-mechanical manufacture of structured surface.
As polarizers for large apertures usually dichroitic foils, beam splitter cubes with dielectric layers or calcite crystals are considered. Polarization foils have the disadvantage that they absorb the large part of the incident radiation which with irradiation of a high intensity and in particular with a high UV component leads to a rapid destruction of the molecular structure of the foil. Beam splitter dice and calcite crystals are with large apertures so expensive that an economical application is excluded.
The invention thus concerns itself with a further known phenomena of the polarization of light, that is the polarization by optical refraction and reflection on refractive surfaces, in particular of preferably plane-parallel glass plates.
The light components of s-polarization and p-polarization are refracted with differing strength and reflected with differing intensity components.
For the differing intensity components the equations according to Fresnel apply from which there follows that the reflection of the p-polarization disappears at the so-called Brewster angle, the reflected light thus only comprises an s-polarization component. Also with incident angles which deviate by several degrees from the Brewster angle the reflection component of the p-polarization disappears almost completely. It is therefore sufficient when the angle of incidence lies in the region of the Brewster angle.
From GB 2 272 277 A there is known a device for the s-polarization of light by way of an arrangement of plane-parallel plates at a Brewster angle, wherein the plates stand next to one another at a large distance in order to irradiate a large as possible area of an optical display with polarized light. The large number of plates at the same times serves the enlargement of the irradiated surface. The light reflected by the plates is, after a further reflection, guided back to a mirror in the beam path in order to achieve the s-polarization.
The intensity component reflected at the Brewster angle is free from p-polarization and is therefore completely s-polarized, however only uses a smaller part of the possible intensity. With glass with a refractive index of n=2 the Brewster angle is calculated at 64.degree. and the reflected component of the s-polarization at 64.degree. is calculated at 36%. In comparison with this polarization foils achieve 70%, calcite crystalls 95% and beam splitter dice even 98%.
If in contrast one wishes to use the component of p-polarization transmitted at 100% (theoretically) at the Brewster angle, then one has the disadvantage that also a larger part (in our example with only one refractive surface: 64%) of the s-polarization is transmitted. One therfore has in the transmitted beam not even an approximate complete polarization.